Abstract

Objectives The aim of this study was to assess the impact of ticagrelor dosing regimens on pharmacodynamic (PD) profiles in patients on maintenance ticagrelor therapy.

Background Many patients on maintenance P2Y12-inhibiting therapies may require coronary revascularization procedures, raising a common clinical question with regard to the dosing regimen of the P2Y12-inhibiting agent to be used. To date, investigations assessing dosing regimens of P2Y12 receptor inhibitors in patients on maintenance therapy have been only assessed with thienopyridines, but not with ticagrelor.

Results There were no differences in baseline levels of platelet reactivity with all assays. Intergroup comparisons by means of repeated-measures analysis adjusted for baseline PRI values showed that the LD group had significantly lower PRI levels compared with the MD group during the overall study time course (p = 0.031). Consistent findings were found for P2Y12 reaction unit (p = 0.026) and light transmittance aggregometry (p = 0.004). Intragroup comparisons showed that a more prompt and sustained platelet inhibitory effect was achieved more consistently with an LD regimen compared with a MD regimen.

Conclusions In patients on maintenance ticagrelor therapy, a 180-mg LD regimen of ticagrelor is associated with more potent and prompt platelet inhibition compared with a 90-mg MD. (Impact of Ticagrelor Re-Load Pharmacodynamic Profiles; NCT01731041).

Dual antiplatelet therapy (DAPT) with aspirin and a P2Y12 receptor inhibitor is the recommended therapy for secondary prevention of ischemic events in patients with acute coronary syndrome (ACS) and those patients undergoing percutaneous coronary interventions (PCIs) (1–3). Ticagrelor represents a new class of oral nonthienopyridine P2Y12 receptor inhibitor, called a cyclopentyltriazolo-pyrimidine. Compared with clopidogrel, ticagrelor has reversible binding properties and more prompt and potent pharmacodynamic (PD) effects as well as less variability in interindividual response (4–7). In a large-scale clinical trial of ACS patients, ticagrelor was associated with a significant reduction in ischemic events, including cardiovascular mortality, compared with clopidogrel at 12 months (8). Such benefit was observed irrespective of management strategy (invasive or noninvasive) and occurred without any differences in overall major bleeding complications, although noncoronary artery bypass graft bleeding events were increased with ticagrelor. Despite such benefit, recurrent atherothrombotic events still occur in ticagrelor-treated patients who may also require PCI (8,9). Moreover, many patients receiving maintenance ticagrelor therapy may need revascularization because of coronary atherosclerotic disease progression or for staged PCI (10,11).

Numerous investigations have been conducted to define the dosing regimen associated with more favorable PD effects in patients on maintenance P2Y12-inhibiting therapy using thienopyridines (12–17). In particular, reloading patients on maintenance clopidogrel therapy is associated with additional platelet inhibition (12–14). This was also demonstrated among prasugrel-treated patients, suggesting that a sizable number of P2Y12 receptors remain uninhibited during maintenance therapy even with a more potent agent (15,16). However, there are substantial differences in the pharmacological properties between ticagrelor and thienopyridines (4–7), and whether PD profiles vary according to the dosing regimen administered in patients on maintenance ticagrelor therapy remains unexplored. Therefore, we conducted a study to assess the PD effects of different ticagrelor dosing regimens in patients on ticagrelor maintenance therapy.

Methods

Study population and research design

This was a prospective, randomized, double-blind, placebo-controlled PD study conducted in patients on maintenance ticagrelor therapy (NCT01731041). All patients had experienced an ACS and a guideline-based indication to be on DAPT with aspirin and ticagrelor (1–3). Patients were screened at the Division of Cardiology of the University of Florida College of Medicine – Jacksonville. All patients were eligible for the study if they were between 18 and 80 years of age and if they were receiving treatment with low-dose aspirin (<100 mg/day) and ticagrelor (90 mg/bid) for at least 14 days as part of their standard treatment regimen. Exclusion criteria included history of intracranial bleeding, severe hepatic impairment (hepatic enzymes >2.5 times the upper limit of normal), active bleeding or propensity to bleed, recent (<14 days) antiplatelet treatment with a glycoprotein IIb/IIIa antagonist, platelet count <80 × 106/ml, hemodynamic instability, glomerular filtration rate <30 ml/min, on treatment with any oral anticoagulant, patients with sick sinus syndrome or second- or third-degree atrioventricular block without pacemaker protection, drugs interfering with CYP3A4 metabolism (ketoconazole, itraconazole, voriconazole, clarithromicin, nefazodone, ritonavir, saquinavir, nelfinavir, indinavir, atazanavir, and telithromizycin), hemoglobin <10 g/dl, and pregnant and lactating females.

Using a computer-based randomization system, patients were randomized in a 1:1 fashion to 1 of 2 treatment groups: 1) 90-mg dose of ticagrelor (maintenance dose [MD] group); 2) 180 mg of ticagrelor (loading dose [LD] group). Patients randomized to the MD group received 1 ticagrelor 90-mg tablet and 1 matching placebo tablet. Patients randomized to the LD group received 2 ticagrelor 90 mg tablets. Ticagrelor 90-mg tablets and matching placebo were provided by AstraZeneca (Wilmington, Delaware). Investigators, laboratory personnel, and patients were blinded to treatment assignments. PD assessments were performed at 3 time points using 3 different assays as described in the following. After completing the study, patients resumed their standard ticagrelor 90 mg twice-daily dosing regimen at their scheduled times. Adverse events, including bleeding, bradyarrhythmias, and dyspnea, were recorded (8). Patients received a follow-up phone call the following day to confirm that no adverse events had occurred.

Blood sampling and platelet function assays

Blood samples were collected at 3 time points at baseline (while on maintenance ticagrelor therapy) and at 1 h and 4 h after randomized treatment. Baseline blood samples were collected 12 ± 2 h after the last MD of ticagrelor to assess trough levels of platelet reactivity (18). At each time point, PD assessments were conducted using 3 different platelet function assays: whole-blood vasodilator-stimulated phosphoprotein (VASP), VerifyNow system (VN-P2Y12), and light transmittance aggregometry (LTA) (7,15,18). In brief, VASP phosphorylation was measured by quantitative flow cytometry using commercially available labeled monoclonal antibodies according to standard protocols (Biocytex Inc., Marseille, France) and quantified by the platelet reactivity index (PRI). The VN-P2Y12 assay (Accriva, San Diego, California) measures platelet-induced aggregation as an increase in light transmittance and reports results in P2Y12 reaction units (PRUs). LTA was conducted using platelet-rich plasma by the turbidimetric method in a 2-channel aggregometer (Chrono-Log 490 Model, Chrono-Log Corp., Havertown, Pennsylvania) after 20 μM adenosine diphosphate (ADP) stimuli and the percentage of aggregation recorded at 6 min.

Sample size calculation and study endpoints

The primary endpoint of the study was the comparison in the PRI determined by VASP between baseline and 4 h after dosing in each arm of treatment. Assuming an absolute 10% difference in VASP-PRI between baseline and 4 h with a common SD of 14%, 28 patients need to be enrolled in each arm to obtain a 95% power and a 2-sided alpha of 0.05. Considering a possible dropout rate of ∼5% to 10%, we estimated that a total of 60 patients needed to be randomized to ensure that complete data would be available for analysis. A cutoff of 10% absolute change in PRI was chosen because this has been associated with a 44% relative reduction of thrombotic events in patients undergoing PCI (19). Additional analysis assessing intergroup and intragroup PD differences using the VN-P2Y12 and LTA were also conducted.

Statistical analysis

Conformity to the normal distribution was evaluated for continuous variables with the Kolmogorov-Smirnov test. For baseline characteristics, continuous variables are expressed as mean ± SD or median (interquartile range) where appropriate, and categorical variables are expressed as frequencies and percentages. The Student t test or Mann-Whitney U test was used to compare continuous variables where appropriate. The chi-square or Fisher exact test (if expected value in any cell was <5) were used to compare categorical variables between the 2 groups. The comparison of platelet reactivity at baseline was performed with a univariate analysis of variance with a general linear model. An analysis of covariance (ANCOVA) method with a general linear model, using the baseline value of platelet reactivity as a covariate, was used to evaluate all other between-group comparisons. A mixed between-within subjects ANCOVA was conducted with a general linear model to assess the impact of the 2 different treatments on platelet reactivity across time points using baseline platelet reactivity levels as covariate. A repeated-measures analysis of variance (ANOVA) model was used to evaluate intragroup comparisons. A 2-tailed p value <0.05 was considered to indicate a statistically significant difference for all the analyses performed. Results are reported as least-square mean ± SE for these detailed analyses. Statistical analysis was performed using SPSS version 22.0 software (SPSS Inc., Chicago, Illinois).

Results

Patient population

Between January 2013 and April 2014, a total of 106 patients with a previous ACS on maintenance ticagrelor therapy were identified. Of these, 65 patients provided written consent to participate in the study; 5 patients withdrew after screening. Therefore, a total of 60 patients on maintenance ticagrelor 90 mg bid therapy were included. These patients were randomized to either a 90 mg (n = 30; MD group) or 180 mg (n = 30; LD group) dose of ticagrelor. Patient disposition is summarized in Figure 1. Baseline characteristics of the study population are summarized in Table 1. There were no differences in baseline characteristics between groups. No adverse events were reported.

Pharmacodynamic findings

There were no significant differences between groups in baseline platelet reactivity as assessed by VASP-PRI (p = 0.350). Repeated-measures analysis adjusted for baseline PRI values showed that the LD group had significantly lower PRI levels compared with the MD group (ANCOVA, p = 0.031) (Online Figure 1). PRI levels at 1 h were not significantly different between groups (p = 0.117), whereas the PRI levels at 4 h were significantly lower in the LD group compared with the MD group (p = 0.012) (Online Figure 1).

Intragroup Comparisons of Platelet Reactivity Index Across Time Points

(A) Intragroup comparisons of whole-blood vasodilator-stimulated phosphoprotein platelet reactivity index (VASP-PRI) across time points in the ticagrelor 90 mg group. (B) Intragroup comparisons of VASP-PRI across time points in the ticagrelor 180 mg group. Data are presented as least square means. Error bars indicate SE. Analysis of variance (ANOVA) p value refers to the overall difference in VASP-PRI in each group. The p values are provided for intragroup comparisons between each time points.

VerifyNow P2Y12 assay. P2Y12 reaction units

There were no significant differences in baseline PRU between groups (p = 0.448). In the intergroup comparison adjusted for baseline value, PRU values were significantly reduced in the LD group compared with the MD group during the overall time course (ANCOVA, p = 0.026) (Online Figure 2). At 1 h, PRU levels were nonsignificantly lower in the LD group compared with the MD group (p = 0.128), but were significantly reduced at 4 h (p = 0.006) (Online Figure 2).

(A) Intragroup comparisons of VerifyNow P2Y12 reaction units (VN-PRU) across time points in the ticagrelor 90 mg group. (B) Intragroup comparisons of VN-PRU across time points in the ticagrelor 180 mg group. Data are presented as least square means. Error bars indicate SE. Analysis of variance (ANOVA) p value refers to the overall difference in VN-PRU in each group. The p values are provided for intragroup comparisons between each time points.

Light transmittance aggregometry

There were no significant differences in baseline ADP-induced platelet aggregation between groups (p = 0.213). The adjusted intergroup comparison showed a significant reduction of ADP-induced platelet aggregation in the LD group compared with the MD group during the overall time course (ANCOVA, p = 0.004) (Online Figure 3). Intergroup comparisons showed a nonsignificant reduction in ADP-induced platelet aggregation in the LD group compared with the MD group at 1 h (p = 0.155), which reached statistical significance at 4 h (p < 0.001) (Online Figure 3).

Intragroup Comparisons of ADP-Induced Platelet Aggregation Across Time Points

(A) Intragroup comparisons of ADP 20 μM-induced platelet aggregation measured by light transmission aggregometry (LTA) across time points in the ticagrelor 90 mg group. (B) Intragroup comparisons of ADP 20 μM-induced platelet aggregation measured by LTA across time points in the ticagrelor 180 mg group. Data are presented as least square means. Error bars indicate SE. Analysis of variance (ANOVA) p value refers to the overall difference in platelet aggregation in each group. The p values are provided for intragroup comparisons between each time points.

Discussion

The need for coronary revascularization despite being compliant with P2Y12-inhibiting therapy may occur for a variety of reasons, including treatment failure with the occurrence of an acute ischemic event, the need for a staged PCI, or progression of coronary atherosclerotic disease (9–11). This therefore raises a clinical question with regard to the dosing regimen of a P2Y12-inhibiting agent to be used in a patient on maintenance DAPT therapy. To date, investigations assessing dosing regimens of P2Y12 receptor inhibitors in patients on maintenance therapy have been limited to thienopyridines but not the nonthienopyridine ticagrelor (12–17). We therefore conducted a study to address the impact of 2 different ticagrelor dosing regimens in patients on a standard 90-mg bid maintenance therapy. Our PD investigation showed that compared with a 90-mg dose, a 180-mg reloading dose of ticagrelor is associated with enhanced platelet inhibition in patients on maintenance therapy. Furthermore, enhanced platelet inhibitory effects were achieved promptly with this regimen. Importantly, consistent findings were observed using 3 different PD assays.

Currently, practice guidelines provide limited recommendations with regard to the management of patients already on maintenance P2Y12 receptor–inhibiting therapy undergoing PCI or presenting with an ACS (1–3). Various studies have been conducted to assess the impact of different dosing regimens of P2Y12 receptor inhibitors, either reloading with the same agent or switching therapy, in patients on maintenance therapy (20). A ≥600-mg LD of clopidogrel has been shown to reduce residual platelet reactivity in patients on long-term clopidogrel therapy, as well as decrease peri-PCI ischemic complications, particularly in ACS patients (12–14). The fact that clopidogrel therapy is associated with only modest P2Y12 receptor occupancy explains why switching to either prasugrel or ticagrelor leads to further platelet blockade (21–26). Importantly, although randomized studies specifically designed to assess the clinical impact of switching from clopidogrel to a novel P2Y12 receptor inhibitor are lacking, nearly one-half the patients randomized to ticagrelor in the landmark PLATO (Study of Platelet Inhibition and Patient Outcomes) trial were pre-treated with clopidogrel, showing consistent findings with the overall trial results (27). Moreover, many registries have supported the efficacy and safety of switching from clopidogrel to prasugrel (28–31).

The PD impact of administering escalating prasugrel dosing regimens in patients on standard maintenance therapy has been recently reported, demonstrating that a 60-mg LD of prasugrel induces more prompt and potent reduction in platelet reactivity, with better response profiles, compared with lower dosing regimens (15,16). These study findings also suggest that maintenance therapy with a potent P2Y12–inhibiting agent such as prasugrel still leaves a considerable number of P2Y12 receptors uninhibited. This is in line with in vitro and ex vivo PD investigations using cangrelor in which residual P2Y12-mediated signaling in patients on maintenance prasugrel therapy is virtually abolished (32,33). However, ticagrelor has several pharmacological differences compared with thienopyridines. In particular, ticagrelor is direct acting with reversible binding and has a plasma half-life of 6 to 13 h requiring twice-daily administration to maintain steady-state levels of platelet inhibition (4–7). In contrast to the thienopyridines, which require LD regimens that are several fold higher than their MD (e.g., 4- to 8-fold higher for clopidogrel and 6-fold higher for prasugrel), the LD of ticagrelor is the same as the total daily MD. Therefore, although the enhanced PD differences observed with LD regimens of thienopyridines may be intuitive, this is less obvious for ticagrelor and provides further support for the rationale of our investigation.

Clinical implications

Although our study was not designed to assess clinical outcomes, there are potential clinical implications of this investigation. In fact, achieving enhanced platelet inhibition in the peri-PCI period reduces ischemic events, in particular when optimizing blockade of the P2Y12 receptor signaling pathway (34,35). This is supported by large-scale clinical trial data showing a significant reduction in myocardial infarction and stent thrombosis in the peri- and post-PCI period associated with the potent P2Y12 receptor inhibitor cangrelor (36–38). Our study findings clearly demonstrate more prompt and potent P2Y12 inhibition when a 180-mg reloading dose of ticagrelor is administered to patients on maintenance therapy. In turn, this also indicates that uninhibited P2Y12 receptors persist on the platelet membrane of patients while on maintenance therapy. This observation is also supported by ex vivo PD investigations conducted in ticagrelor-treated patients in which residual P2Y12-mediated signaling is markedly reduced by cangrelor (39). Importantly, uninhibited P2Y12 receptors may represent a pathway for circulating ADP, released during an acute ischemic event or during a revascularization procedure, to activate platelets and lead to a periprocedural ischemic complication. Therefore, administration of a 180-mg LD of ticagrelor may be a more optimal strategy than using a 90-mg dose in patients on maintenance therapy requiring PCI or presenting with an acute coronary event. It may be argued that in another study, there were no PD differences between a 90-mg and a 180-mg dose in clopidogrel-treated patients (40). However, this study was conducted in patients with optimal response to clopidogrel, which may have limited the ability to see a treatment effect and was in contrast with a more detailed PD investigation that demonstrated enhanced platelet inhibitory effects of a 180-mg LD irrespective of clopidogrel responsiveness (25).

Study limitations

This investigation was powered to assess intragroup comparisons but not intergroup comparisons. Therefore, the latter results should be considered as exploratory. In addition, our study was conducted in patients who were clinically stable after experiencing an ACS and not in patients undergoing PCI who may therefore share different PD profiles. Moreover, our study was not powered to assess safety or efficacy, which would require larger clinical studies. Hence, the lack of adverse events, including bleeding complications (e.g., arterial access site complications), in this study should be interpreted with caution.

Conclusions

In patients on maintenance ticagrelor therapy, a 180-mg LD of ticagrelor is associated with more prompt and potent PD effects compared with a 90-mg dosing regimen. Although the clinical implications of our PD study findings remain to be demonstrated, achieving enhanced P2Y12 receptor blockade in the peri-PCI period is well established to reduce ischemic events, suggesting the use of a 180-mg reloading dose of ticagrelor in patients on maintenance therapy when undergoing PCI. Clinical outcomes studies are warranted to support these PD findings.

Perspectives

WHAT IS KNOWN? Ticagrelor is a new-generation P2Y12 receptor inhibitor associated with better clinical outcomes compared with clopidogrel. However, many patients on maintenance P2Y12-inhibiting therapies, including ticagrelor, may need to undergo coronary revascularization procedures, raising a common clinical question with regard to the dosing regimen to be used.

WHAT IS NEW? Our study findings demonstrate that in patients on standard maintenance ticagrelor therapy, a 180-mg reloading dose achieves more prompt and potent P2Y12 inhibition compared with a 90-mg dosing regimen as assessed by multiple pharmacodynamic assessments.

WHAT IS NEXT? Because enhanced platelet inhibition in the periprocedure period reduces ischemic events, larger studies are needed to support the clinical impact of these pharmacodynamic findings.

Appendix

Appendix

For supplemental figures, please see the online version of this article.

Footnotes

The present study was funded by an investigator-initiated grant from AstraZeneca. AstraZeneca had no role in the analysis, study design, or decision to publish these results. Dr. Angiolillo has received consulting fees or honoraria from Eli Lilly, Daiichi Sankyo, The Medicines Company, AstraZeneca, Merck, Abbott Vascular, Sanofi, Bayer and PLx Pharma; has participated in review activities for CeloNova, Johnson & Johnson, and St. Jude Medical; and has received institutional payments for grants from Gilead, GlaxoSmithKline, Eli Lilly, Daiichi Sankyo, The Medicines Company, Osprey Medical, Inc, Janssen Pharmaceuticals, Inc, Novartis, CSL Behring, and AstraZeneca. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.

Abbreviations and Acronyms

ACS

acute coronary syndrome

ADP

adenosine diphosphate

ANCOVA

analysis of covariance

ANOVA

analysis of variance

DAPT

dual antiplatelet therapy

LD

loading dose

LTA

light transmittance aggregometry

MD

maintenance dose

PCI

percutaneous coronary intervention

PD

pharmacodynamic

PRI

platelet reactivity index

PRU

P2Y12 reaction units

VASP

whole-blood vasodilator-stimulated phosphoprotein

Received December 9, 2014.

Revision received February 16, 2015.

Accepted February 18, 2015.

2015 American College of Cardiology Foundation

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